Recent studies have suggested that high levels of endotoxin exposure during infancy are associated with a reduced risk of subsequent allergic sensitivity. Learning more about the relationship between environmental endotoxin exposure and subsequent allergic disease is potentially important given the increasing prevalence of allergic diseases in the United States. The goal of this application is to evaluate the hypothesis that high levels of environmental endotoxin exposure will be associated with reduced anti-tetanus IgE responses following routine immunizations with tetanus toxoid in infancy. This study will utilize the structure of the ongoing WHEALS Study (AI/ES 50681, a study to evaluate the hygiene hypothesis in a multi-racial birth cohort of 3000 children in and around Detroit, MI). In home endotoxin assessements will be increased from 1 to 5 locations (the floor beside the infant's crib, the infant's bed, the parent's bed, the floor beside the parent's bed, and the floor in the living/family room) during both the 1 and 6-month home visits. Endotoxin will be measured using a commercial kinetic Limulus assay. Relationships between endotoxin measurements by location, month of year, and household characteristics (e.g., animals in the home) will be examined. These analyses will provide a better understanding of variations in endotoxin exposure within homes and allow an assessment of whether measurements from certain locations are more closely related to altered IgE production. All infants in this cohort are expected to receive routine immunizations with DtaP (diphtheria, tetanus and acellular pertussis) vaccine at 2,4, 6-7 and 15-18 months of age. In addition to measuring IgE specific for common allergens at 6 and 24 months of age, IgE specific for tetanus toxoid will be measured in the same blood samples using the commercial Pharmacia CAP assay. The anti-tetanus IgE measurements will be analyzed to learn whether IgE production is influenced by endotoxin exposure. Important advantages of measuring anti-tetanus IgE are the likelihood that most infants will receive all immunizations with identical doses at the same ages. The well standardized tetanus immunizations contrast with the highly variable and difficult to measure exposures to natural allergens. Anti-tetanus IgE responses are also likely to be measureable much earlier in infancy than are responses to other allergens. [unreadable] [unreadable]